1. Technical Field
The present disclosure relates to a sewing machine which is provided with a cloth feed mechanism for moving a workpiece cloth on a sewing machine bed.
2. Related Art
When a sewing machine which sews a workpiece cloth is used to sew, for example, two cloths in a superimposed or overlapped state, a failure such as a positional shift between the cloths sometimes occurs during sewing. In this case, the user cannot view an underside of the lower workpiece cloth although he or she can view an upper surface of the upper workpiece cloth. In view of the aforementioned failure, sewing machines are provided with a workpiece cloth recognizing device which detects the shift between the workpiece cloths by imaging the workpiece cloths from above and from below by an imaging unit when workpiece cloths are sewn in the superimposed state.
Failures other than the aforementioned shift between the superimposed workpiece cloths sometimes occur in stitches on the underside of the lower workpiece cloth during sewing of the workpiece cloths by the sewing machine. Furthermore, another failure in stitches such as bird's nest sometimes occurs in sewing machines which can sew embroidery patterns on the workpiece cloth. The bird's nest is an entanglement of a needle thread at the underside of the workpiece cloth during the sewing of an embroidery pattern. In a case where the sewing is continued without user's finding the stitch failure, a large amount of thread would thereafter need to be disentangled such that the thread would be wasted. Additionally, disentangling the thread would damage the workpiece cloth. As a result, it is desirable that the failures during the sewing should be early detected.
However, when an imaging unit is disposed in front of a sewing machine bed, the presence or absence of shift between the workpiece cloths is detected at the location ahead of the sewing machine bed. This renders, impossible, detection of the state of the workpiece cloth during or after sewing and the state of stitches at the underside of the workpiece cloth. Furthermore, a cloth feed mechanism, a shuttle mechanism and the like are housed in the bed on which the workpiece cloth is to be placed. This increases the size of the bed when the imaging unit is housed in the bed to image the underside of the workpiece cloth.